Bug 2503674

Summary: CVE-2026-59849 libssh: libssh: denial of service via automatic certificate authentication loop [fedora-all]
Product: [Fedora] Fedora Reporter: Vladimir Vasilev <vvasilev>
Component: libsshAssignee: Andreas Schneider <asn>
Status: CLOSED ERRATA QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: low Docs Contact:
Priority: low    
Version: rawhideCC: ansasaki, asn, jjelen, negativo17, shebburn
Target Milestone: ---Keywords: Security, SecurityTracking
Target Release: ---Flags: fedora-admin-xmlrpc: mirror+
Hardware: Unspecified   
OS: Unspecified   
Whiteboard: {"flaws": ["87e800dc-fbf1-44ec-bad5-54f27f011218"]}
Fixed In Version: libssh-0.11.5-1.fc43 libssh-0.12.1-1.fc44 Doc Type: ---
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2026-07-23 01:03:36 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 2498182    

Description Vladimir Vasilev 2026-07-21 15:15:19 UTC 
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

A flaw was found in libssh automatic certificate-based public key authentication. In ssh_userauth_publickey_auto() in src/auth.c, the iterator over certificate candidates was not advanced correctly when configured certificates were missing or repeatedly rejected by the server. Under specific non-default certificate configurations, this could cause the client to restart the same authentication attempts indefinitely, leading to denial of service.
Comment 1 Fedora Update System 2026-07-22 09:32:52 UTC 
FEDORA-2026-0e46c91ccf (libssh-0.12.1-1.fc44) has been submitted as an update to Fedora 44.
https://bodhi.fedoraproject.org/updates/FEDORA-2026-0e46c91ccf
Comment 2 Fedora Update System 2026-07-22 09:33:50 UTC 
FEDORA-2026-063caa9112 (libssh-0.11.5-1.fc43) has been submitted as an update to Fedora 43.
https://bodhi.fedoraproject.org/updates/FEDORA-2026-063caa9112
Comment 3 Fedora Update System 2026-07-23 01:03:36 UTC 
FEDORA-2026-063caa9112 (libssh-0.11.5-1.fc43) has been pushed to the Fedora 43 stable repository.
If problem still persists, please make note of it in this bug report.
Comment 4 Fedora Update System 2026-07-23 01:20:29 UTC 
FEDORA-2026-0e46c91ccf (libssh-0.12.1-1.fc44) has been pushed to the Fedora 44 stable repository.
If problem still persists, please make note of it in this bug report.